1. Field of the Invention
The present invention relates to a functional thin film member suitable for use in optical switches, light modulators, highly integrated circuits, infrared light sensors, ultrasonic sensors, micro-actuators, electroluminescence elements, high speed transistors, and low-resistance wiring members.
2. Discussion of Background
Conventional functional devices are composed of a substrate made of a single crystal and a single crystal thin film layer made of a variety of oxides formed on the substrate. Such functional devices, however, are difficult to apply to a functional device with a large functional area required for giant electronics. For example, a 10-inch Si wafer is produced at present. However, 6-inch to 8-inch Si wafers are in general use. From the viewpoint of the concept of machine-interface, devices with sizes corresponding to A.sub.5 to A.sub.0, and B.sub.5 to B.sub.0 sheets are necessary. However, the maximum size that can be obtained by a conventional single crystal formation technique is 10 inch. In other words, it is extremely difficult to obtain a wafer with a size of more than 10 inch by the conventional single crystal formation technique.
Furthermore, it is extremely difficult to form a thin film layer of an oxide on a substrate which contains at least one atom component of Si or Ge by the conventional method. This is because each of a Si-substrate and a Ge-substrate has a very stable oxide film layer on the surface thereof when exposed to air at room temperature. Even if such an oxide film layer is removed from the substrate, Si or Ge is oxidized again during the formation of such an oxide thin film layer, so that such an oxide thin film layer does not undergo epitaxial growth. In order to solve this problem, the following methods are mainly employed conventionally:
(1) A method of formation an oxide thin film layer at a temperature at which the oxide layer is evaporated.
(2) A method of causing a gas which etches an oxide thin film layer to flow in the course of the formation of the oxide thin film layer, whereby a competitive reaction between the etching reaction and the deposition of the oxide thin film is caused to occur.
However, these methods have the shortcomings that the temperature necessary for carrying out these methods is high and the controlling of the processes is difficult, so that it is difficult to form an oxide thin film layer in a stable manner.